1. Technical Field
The present invention relates to a measuring unit, a measuring system and a method for determining a relative position and relative orientation. The present invention relates in particular to a measuring unit and a method for determining a relative position and relative orientation using electromagnetic radiation.
2. Background Information
The measurement of a location and orientation of an object in a three-dimensional space has various applications, for example in industrial production or in quantitative quality control, in particular in industrial production. Tactile coordinate measuring machines, for example, may be used in quantitative quality control which can attain high precisions in volumes of a few cubic meters; however, the position of a measuring probe must be determined with a corresponding accuracy. Other applications for determining the location of an object relative to a reference system include robot kinematics in industrial production or measurement, in which at least some elements of the robot kinematics have three translatory and three rotatory degrees of freedom. In such and other apparatuses it is required to determine the location of a component of the system in space. For determining the location, both the position of a predetermined point of the component relative to a fixed point and the orientation of a coordinate system defined by the component relative to a stationary reference system in the laboratory must be known. For example, for a coordinate measuring machine it is required that the location, i.e. the position and orientation of a measuring head in a space, can be determined with high accuracy. Calibration techniques may be used to this end, as described in U.S. Pat. No. 6,611,346 B2.
It is a challenge to determine the position and orientation of an object in space in an accurate manner. Techniques using electromagnetic radiation, in particular optical techniques using radiation with wavelengths in the IR, visible or UV part of the electromagnetic spectrum are attractive with regard to their accuracy and the device complexity required for determining the location.
Methods for determining the location of an object using electromagnetic beams, in particular optical beams, are described in U.S. Pat. No. 7,358,516 B2 and U.S. Pat. No. 4,621,921, for example. In U.S. Pat. No. 4,621,926, at least five interferometers are used in total to track and control the movement of an object on a non-linear path. In the method described in U.S. Pat. No. 7,358,516 B2 a beam cone is respectively emitted from one point or from plural points which simultaneously covers plural reflectors. Controllable shutters or other techniques may be used to attain unambiguousness between the point of origin of the beam cone and the reflector.
There is a continued need for devices and methods with which a position and orientation of an object relative to a reference frame may be determined using electromagnetic radiation. In particular, there is a need for such devices and methods in which problems relating to the unique allocation of elements between which a length was measured may be mitigated. There is further a need for such devices and methods which allow the location of the object to be reliably determined for a wide range of different locations of the object without requiring the location of the object to be changed for this purpose.